1. Field of the Invention
The present invention relates to an electrochromic mirror that is used for, for instance, for rear-view, an outer mirror or an inner mirror of a vehicle and capable of varying the reflectance by applying a voltage thereto.
2. Description of the Related Art
As a vehicular outer mirror or inner mirror, an electrochromic mirror (in some cases, referred to as an “anti-glare mirror”) is used that varies the transmittance of light incident on a reflective film or light reflected by that an electrochromic film formed on a surface of the reflective film is colored.
In the electrochromic mirror like this, an electrochromic film is formed of tungsten trioxide or the like. Furthermore, in this kind of electrochromic mirror, a cell in which an electrolytic solution including lithium ions is encapsulated between a pair of electrodes is used. When a predetermined voltage is applied between electrodes of the cell to occur reduction reaction for tungsten trioxide with lithium ions in the electrolytic solution and electrons fed from the electrode, the electrochromic film is colored substantially blue.
In the electrolytic solution in the cell, other than lithium ions, ferrocene and the like is included as oxidation-reduction (redox) agent. When a predetermined voltage is applied between a pair of electrodes as mentioned above, ferrocene is oxidized at an anode of the pair of electrodes to form a positive ferrocene ion. The ferrocene ion is, upon reaching a cathode of the pair of electrodes, reduction-reacted (reduced) to return to ferrocene.
When the oxidation reaction and reduction reaction of the ferrocene like this are repeated, a steady current flows between the electrodes. On center sides of the respective electrodes, a current such as mentioned above in the circumference flows to cause a voltage drop; as a result, a portion corresponding to the center side (that is, center side of the cell) of the respective electrodes in the electrochromic film is not sufficiently colored in some cases.
One measure for solving such a phenomenon is disclosed in JP-A No. 2005-321521 (a patent document 1). In the patent document 1, when respective values of the electric conductivity σ of the electrolytic solution that constitutes an electrochromic cell used for an electrochromic mirror, an area resistance value R of a pair of electrodes, a length L of the electrodes and a distance h between electrodes are set so that a numerical value α obtained when these values are inserted in a formula (1) below is 2 or less, uniformity of a distribution of a voltage applied to the electrolytic solution is improved.α=(σ·R/h)1/2  (1)
However, there are restrictions on material of electrode and electrolytic solution, electrode dimension based on dimensions of the respective portions as a whole of mirror, and the like. As the result, it is practically difficult to set the above mentioned respective values so that a value of α that is a calculation result of the formula (1) is 2 or less.